1. Technical Field
The present invention relates to a printer that conveys roll paper pulled from a paper roll stored in a roll paper compartment passed the printing position of a printhead by means of a paper feed roller and prints. More particularly, the invention relates to a printer that guides recording paper to the paper feed roller while maintaining specified tension on the recording paper by means of an elastically displaceable tension guide in order to reduce variation in the feed load on the paper feed roller.
2. Related Art
In printers that print on roll paper delivered from a paper roll, the paper feed load on the paper feed roller changes greatly according to variation in the inertial weight of the paper roll, for example, and can easily cause the roll paper feed precision to vary. For example, if the paper feed precision varies when printing a barcode with precise spacing, the thickness of the bars and the spaces between bars varies if the paper feed precision changes, and it may not be possible to print a barcode that can be accurately read. To solve this problem, Japanese Unexamined Patent Appl. Pub. JP-A-2009-269399 teaches a method of guiding the recording paper delivered from a paper roll to the paper feed roller while maintaining specific tension on the recording paper by means of an elastically displaceable tension guide, and using this elastic displacement of the tension guide to suppress variation in the roll paper feed load acting on the paper feed roller.
Different types of recording paper are also known. There is, for example, recording paper for creating wrist bands that are attached and worn around the patient's wrist or ankle in hospitals as described in Japanese Unexamined Patent Appl. Pub. JP-A-2005-133265. This recording paper is a narrow band of a constant width that can be cut to a certain length, and is used as a wrist band after printing the required information using an inkjet printer, for example, and then cutting the paper to length. This type of recording paper can also be supplied in rolls.
In addition to having different widths, the recording paper can thus be made of different materials, have a coated surface, and vary in other ways. Recording paper for making wrist bands, for example, may be made from a non-woven cloth, and the back side that is worn against the patient's skin may be surface treated to increase the friction coefficient for greater comfort and prevent the wrist band from slipping, for example. The recording paper may be coated with a high friction coefficient material, for example, or be treated to increase surface roughness and improve sliding resistance.
Problems such as described below can result in a printer that guides the recording paper to the paper feed roller while maintaining tension on the recording paper by means of a tension guide when printing on recording paper with different surface characteristics, particularly different friction coefficients.
For example, because the friction coefficient is higher when conveying recording paper for making wrist bands than when conveying plain recording paper, sliding resistance between the recording paper and the paper feed guide is high. More specifically, because the tension guide urges the recording paper with a specific elastic force, the sliding resistance is much greater than other recording paper guide parts inside the printer. When the friction coefficient of the recording paper is high, the sliding resistance with the tension guide may exceed the paper feed force of the paper feed roller, and it may not be possible to feed the recording paper.